1. Field of the Invention
This invention relates to an ink tank for retaining ink.
The invention also relates to an ink jet recording head of cartridge type, in which an ink tank and a recording head section are integrally accommodated in a housing, and which can be mounted on and dismounted from a recording apparatus.
The invention further relates to an ink jet recorder with such an ink jet recording head.
2. Related Background Art
As an ink jet recording head, in which an ink discharge section for discharging recording liquid (hereinafter referred to as "ink") for recording and an ink tank or reservoir containing the ink to be supplied to the ink discharge section are integrally accommodated in a housing, there are those shown in U.S. Pat. Nos. 3,953,862 and 4,095,237 and also there is one as shown in FIGS. 1A and 1B.
In the recording head shown in the U.S. Pat. No. 3,953,862, a water-repellent filter is provided in an air-communication hole of an ink tank.
The filter in this recording head, however, is disposed in a plug constituting an air-communication port such that it is found on the inner surface of the ink tank. Therefore, the head has problem of leakage of ink through a gap between the plug and ink tank body and also those concerning the continued effect of the water-repellent filter.
In the recording head shown in the U.S. Pat. No. 4,095,237, ink is retained by an ink carrier, and the neighborhood of an air-communication hole is provided with no means against ink leakage. Therefore, ink leakage may occur. In addition, it is liable that air reaches the recording head through a gap between the ink carrier and ink tank, resulting in instable discharge of ink.
In the ink jet recording head shown in FIGS. 1A and 1B, which is generally designated at 101, an ink containing section (hereinafter referred to as "ink tank") 102 and an ink discharge section (or also referred to as "recording head section") 103 having a function of discharging ink are constructed integrally. The ink discharge section 103 has an ink discharge port provided in an ink discharge face thereof. The ink tank 102 consists of a housing 106 as an outer cover and a lid 107. In the ink tank 102, a porous material 108 is accommodated as ink carrier in the ink tank 102 to prevent ink from being moved or leaking to the outside when the ink tank experiences sudden shocks or the like. An ink-carrying section 109 of the porous material 108 is impregnated with ink, so that ink can be supplied to the ink discharge section 103. Reference numeral 110 designates a vent hole communicating the ink tank 102 with atmosphere. The ink tank inner pressure is held constant by the vent hole 110.
A portion 111 of the porous material 108 on the side of the vent hole 110 is an ink-repellent portion obtained by a repellent treatment. This ink-repellent portion 111 prevents ink from leaking through the vent hole 110 to the outside.
Ink in the ink tank 102 is passed through a filter 105 for separating dust or the like and then supplied to the ink discharge section 103 and discharged through the discharge port 104 by discharge energy generation means (not shown) such as a heat-generating resistor.
As ink in the ink tank 102 is consumed, air is supplied to the ink-carrying portion 109 through the vent hole 110. In this way, the inner pressure of the ink tank is held constant to maintain optimum ink discharge characteristics.
The recording head 101 having the above construction is mounted on a carriage 1111 as shown in FIG. 2, and it is secured to the carriage 1111 by keeping members 1112. While the carriage 1111 is moved along guide bars 1115 by a drive wire 1113 and a drive motor 1114, the recording head 101 discharges ink in a direction of arrows Z for recording on a recording sheet 1116. Reference numeral 1117 designates a platen for supporting the recording sheet 1116, 1118 a sheet feed motor for causing the platen 1117 to feed the sheet, and 1119 flexible wiring for supplying an ink discharge signal to the recording head 101 for recording.
With the above prior art ink jet recording head 101 of integral type, however, ink is retained by impregnating the porous material 108 accommodated in the ink tank 102 with the ink, and also the ink tank 102 has the vent hole 110. Therefore, when the recording head 101 experiences vibrations or shocks, ink carried by the ink-carrying portion 109 is liable to flow into space 114 without being prevented by the liquid-repellent or ink-repellent portion 111, or occasional pressure application to the housing 106 during handling of the recording head 101 may cause leakage of such ink through the vent hole 110, thus contaminating inner and outer portions of the ink jet recording apparatus or hands or clothes of the operator or being attached to an electric connection section (not shown) of the recording apparatus to result in rupture of the recording apparatus.
Further, since the porous material 108 is pressure-loaded in the ink tank 102, it is greatly squeezed, and its porisity is reduced. Therefore, the ink tank has a small ink-retaining capacity, usually 50% or below, despite its large volume. If it is intended to increase the filling amount of retained ink, leakage of ink 109 through the vent hole 110 is liable in such case as when the posture of the head is altered, thus leading to the problems noted above. Further, a large amount of ink remains without being used, that is, the percentage of ink consumption is low in spite of a large ink tank volume, and it is necessary to increase the volume of the ink tank in order to ensure a large amount of ink capable of consumption.
Still further, with the above prior art ink jet recording head 101 of integral type, bubbles of air or the like mixed in ink are liable to be led together with ink in the ink tank 102 to the ink discharge section 103. This has adverse effects on the ink discharge characteristics and will cause defective discharge or failure of discharge of ink. Particularly, such bubbles are led through a gap 114 between the inner wall surface of the ink tank 102 and porous material 108 toward the ink discharge section 103 as shown by arrows A in FIG. 1B. Therefore, it is necessary to block such route of bubbles.
Further problems in the prior art ink jet recording head reside in the air vent hole structure for communicating the ink tank with atmosphere. U.S. Pat. No. 4,306,245 discloses a structure, in which two vent holes communicating an ink tank with atmosphere are provided at predetermined positions on ink tank side wall.
In this structure, a predetermined space is provided between an ink accommodation zone, in which ink is accommodated, and atmosphere, and the ink accommodation zone is communicated with atmosphere through that space and the two vent holes.
In this case, leakage of ink to the outside is readily caused by the tilting or vibrations of the ink tank because of the presence of the two vent holes, causing contamination of the recording apparatus or hands or clothes of the operator and also resulting in waste of ink.
In a further aspect, in a recording head, in which the ink tank and recording head section are constructed integrally, usually an ink passage for leading ink from the ink tank to the ink discharge section and an ink injection passage for sealing ink in the ink tank are provided separately. In case where the ink tank is provided with an ink injection hole, through which ink is supplied, it is liable that ink is attached to the wall of the hole and closes the hole or that the hole wall is wetted to result in dust collection thereon. In either case, stable ink supply is no longer possible.
Besides, where the ink passage for leading ink from the ink tank to the ink discharge section and ink injection passage for sealing ink in the ink tank are provided separately, complicated construction is inevitable, and also it is difficult to reliably fill both the ink tank and ink discharge section with ink.
There is a further prior art structure, in which a porous film is provided at an air-communication port to prevent leakage of ink through the vent hole 110 as noted before. In this case, however, it is liable that pores of the porous film are closed by dried ink to produce a sealed state of the ink tank inside. In such a case, with the progress of recording an excessive burden is produced in the ink tank inside, thus resulting in defective discharge of the ink or the like.